1. Field of the Invention
The present invention relates generally to a disk drive assembly and delay circuitry for time delay compensation of digital data prior to writing it on a magnetic medium.
2. Brief Description of the Related Art
Digital data are written on a magnetic medium by the use of flux transitions. A flux transition is a site of change in the physical orientation of the medium, hence a change in the magnetic flux generated by the medium at that site. When a flux transition is written by a transducing head on the medium in a disk drive assembly it is written in the context of the prior flux transition and the next flux transition. When the flux transition is read back by the head, it will typically be perceived to be at a different interval in time in relation to the prior flux transition and the next flux transition. This phenomenon is known as peak shift, a generic term for the problem addressed by the present invention. Peak shift is a problem because if the change in time interval between flux transitions becomes great enough, the data pattern read back from the magnetic medium may be incorrect, i.e. the flux transition may fall outside of its detection "window".
One conventional method of dealing with peak shift is to administer prewrite compensation when writing a data pattern. This means each flux transition written is moved a short interval of time (early or late) so that the peak shift is minimized or at least lessened in most cases. The problem with this approach is that only one value of prewrite compensation is used even though a range of peak shift values is generally significant with respect to any single value of delay.
The present invention is designed to address this unresolved problem by adaptively compensating for peak shift. Adaptivity is achieved by determining the actual peak shifts promulgated by a given disk drive assembly under certain parameters. The parameters adaptively covered by the present invention are: (1) the head/media pair to be used for writing; (2) the writing site on the disk; and (3) the data pattern to be written.
Of interest is Horie et al., U.S. Pat. No. 4,633,336 which uses prewrite compensation based on the above-mentioned parameters but only in a limited sense. The Horie system determines whether prewrite compensation is appropriate based on the parameters and then simply generates a set value of compensation for each parameter, if appropriate. In contradistinction, the present invention does not use a set value for each parameter but rather a value based on the specific combination of parameters used so that the values generated by the present invention are more variable than the values used by Horie and are applied with much more flexibility.